1. Field of the Invention
The invention relates to a wide-cut, synthetic lubricant base stock synthesized from waxy hydrocarbons produced by a Fischer-Tropsch hydrocarbon synthesis process. More particularly the invention relates to a wide-cut lubricant base stock and formulated lubricating oil having a high VI, low pour point and wide boiling range, produced by hydroisomerizing a waxy Fischer-Tropsch synthesized hydrocarbon fraction, which is then catalytically dewaxed to produce the base stock.
2. Background of the Invention
Internal combustion engine crankcase and transmission oils, as well as some industrial oils, must maintain their lubricating quality over a wide range of temperature without solidifying or volatilizing. The industry is moving toward lighter viscosity grades (e.g., SAE 5W and 10W oils) for fuel economy reasons. However, the oils must also meet volatility specifications. In addition, heavier base stocks, from which fully formulated oils are made, are still utilized in many applications, including industrial oils. With conventional oils, the dewaxed raffinate is typically vacuum fractionated into a plurality of fractions of different viscosities and boiling ranges. The final lubricating oil is made by adding an additive package containing one or more additives such as a VI improver, an antioxidant, a detergent dispersant, antiwear additive, pour point depressant and the like, to the base stock. Lower viscosity base stocks have a higher concentration of lighter and lower boiling hydrocarbons, which tend to volatilize at higher temperatures. Conversely, higher boiling fractions, besides increasing the viscosity, can adversely affect low temperature properties, such as pour point. To use a wide cut derived from a conventional oil, will yield a base stock which will not meet either volatility or pour point requirements. Synthetic base stocks, such as polyalphaolefins (PAO's), are commercially available and have a combination of high viscosity index and low pour point. However, these oils are very expensive, tend to shrink seals and have a narrow boiling range. To be able to use a single, wide-cut oil fraction of lubricating quality as a base stock for a premium lubricating oil, where two or more fractions are now used, would simplify the production, transportation and cost of the oil.